Based on the conventional observation data, mesoscale intensive observation data, satellite and radar products and other data, a comprehensive analysis is made of a hailstorm occurred at the southern foot of the Qilian Mountains on 13 July 2015. The results show: During the process of the Mongolian cold eddy rotation, the cold trough that slid at the bottom moved southeastward to guide the advection of highaltitude cold air and positive vorticity, which, together with the convergence line on the ground, brought the hailstorm to the southern foot of the Qilian Mountains. The large humidity gradient in the north and south and the penetration of cold air in the middle and lower layers induced the greater instability of atmospheric stratification and promoted the stronger vertical upward movement, which provided favorable conditions for the development of severe convection weather. The commashaped hailstorm clouds in satellite images were the main mesoscale system causing hailstorm weather. The radar echo intensity map shows the hailstorm structure characteristics, and the VIL value shows a trend of sharp drops and steep increase, which has a onetoone correspondence with the hailstorm time.